The present invention relates to a gas-tight shut-off valve for a material charging or discharging lock, which is subjected to high operation temperatures.
A standard gas-tight shut-off valve for a material charging or discharging lock of a lock comprises a gas-tight valve housing with an annular valve seat connected thereto and a valve closing element therein associated with this valve seat. The valve closing element is movable between a first position, in which the valve closing element and the annular valve seat can be axially pressed together, and a second position, in which it is located laterally of said discharge opening. A soft sealing means, generally a synthetic seal ring, is mounted either in the annular valve seat or in the valve closing element, so as to provide the required gas-tightness when the valve closing element and the annular valve seat are pressed together.
If such a material charging or discharging lock has to be designed for high working temperatures (e.g. working temperatures above 500xc2x0 C.), the use of a synthetic seal ring in the gas-tight valve constitutes a problem. Indeed, known synthetic seal rings, which are suitable for use in such material lock valves, are only warranted for working temperatures up to 250xc2x0 C.
In order to maintain the working temperature of the seal ring as low as possible, it is known to cool the element containing the groove in which the synthetic seal ring is received and the contact surface on the element against which the synthetic seal ring is pressed. However, when the gas-tight valve is open, the sealing surface of the synthetic seal ring is uncovered by the cooled closing element and therefore directly exposed to heat radiation in the valve housing. Furthermore, as the synthetic seal ring is a very bad conductor of heat, the surface temperature of the exposed sealing surface of the seal ring is not substantially reduced by the cooling of the element containing the groove in which the synthetic seal ring is received. It follows that the exposed sealing surface risks to be damaged if the radiation temperature in the valve housing is substantially higher than the warranted working temperature of the seal ring. This explains whyxe2x80x94despite cooled valve seats and closing elementsxe2x80x94soft sealing means cannot be used if the material charging or discharging lock is to be designed for a working temperature that is substantially higher than the warranted working temperature of available soft sealing means. In such a case, metallic seal rings have to be used, which have however the disadvantage to provide a less good and in particular a less reliable gas-tightness.
The technical problem underlying the present invention is to provide a gas-tight shut-off valve for a material charging or discharging lock in which soft sealing means can be used to achieve gas-tightness between the valve seat and the closing element, despite the fact that the material charging or discharging lock has to be designed for a working temperature substantially higher than the warranted working temperature of the soft sealing means. This problem is solved by a gas-tight shut-off valve as claimed in claim 1.
A gas-tight shut-off valve for a material charging or discharging lock in accordance with the invention comprises in a manner known per se: a valve housing; an annular valve seat connected to the valve housing and surrounding a discharge opening; a valve closing element associated with the valve seat, this valve closing element being movable between a first position, in which the valve closing element and the annular valve seat can be axially pressed together, and a second position in which the valve closing element is located laterally of the discharge opening; means for axially pressing the valve closing element and the annular valve seat together when the valve closing element in its first position; and a soft sealing means associated with the annular valve seat, respectively with the valve closing element, this soft sealing means having an exposed sealing surface to be pressed against a sealing means contact surface on the valve closing element, respectively on the valve seat, for providing gas-tightness when the valve seat and the valve closing element are pressed together. According to an important aspect of the invention, the gas-tight shut-off valve further comprises a heat protecting element that is movable between a first position, in which it covers the exposed sealing surface of the soft sealing means when the valve closing element is in its second position, and a second position in which it uncovers the exposed sealing surface, so as to enable again a gas-tight contact between the exposed sealing surface and the sealing means contact surface. In other words, as soon as the closing element uncovers the exposed sealing surface of the soft sealing means when the valve is opened, the movable heat protecting element is moved over the exposed sealing surface of the soft sealing means, so as to protect the latter against direct heat radiation. Before the valve is closed, the heat protecting element uncovers again the exposed sealing surface of the soft sealing means, so that the latter can fulfil its sealing function between the closing element and the annular valve seat. Thus, the exposed sealing surface of the soft sealing means is efficiently protected against direct heat radiation, as well in the closed valve as in the open valve.
In order to maintain the working temperature of the seal ring as low as possible in the closed valve, the element in which the synthetic seal ring is mounted and the contact surface on the other element against which the synthetic seal ring is pressed are generally cooled. The heat protecting element advantageously also comprises an internal cooling circuit, so as to ensure that the temperature of its surface facing the exposed sealing surface of the soft sealing means is always below the warranted working temperature of the latter.
In a preferred embodiment, the heat protecting element comprises a connection to a gas circuit and gas outlet nozzles located in the heat protecting element, so as to be capable of blowing a gas onto the exposed sealing surface. Thus the heat protecting element is capable of cooling the exposed sealing surface, without being in direct contact with the latter. It will further be appreciated that the gas blown onto the exposed sealing surface cleans the latter from material particles. Thus the heat protecting element also helps to protect the exposed sealing surface against mechanical damages.
In a first embodiment of the gas-tight valve, the soft sealing means is associated with the annular valve seat and the heat protecting element has a discharge opening therein, which is axially aligned with the discharge opening in the annular valve seat when the heat protecting element is in its first position. In this case, the heat protecting element is e.g. a ring-shaped element, which is pivotable about an pivoting axis between its first and second position. This pivoting axis may be parallel to the central axis of the annular valve seat and located laterally of the annular valve seat. Alternatively, the pivoting axis may be perpendicular to the direction of the central axis of the annular valve seat and located laterally of the annular valve seat.
The heat protecting element and the valve closing element may also form a combined closing-heat protecting element, which has a closing portion fulfilling the function of the valve closing element and a heat protecting portion fulfilling the function of the heat protecting element. The heat protecting portion of such a combined closing-heat protecting element has a discharge opening therein, which is axially aligned with the discharge opening in the annular valve seat when the heat protecting portion covers the soft sealing means. Such a combined closing-heat protecting element may e.g. be a spherical or cylindrical element which is pivotable about a pivoting axis that is perpendicular to the central axis of the annular valve seat. Alternatively, it may be a flat plate element which is movable in a plane that is perpendicular to the central axis of the annular valve seat.
A gas-tight shut-off valve with combined closing-heat protecting element may have an annular counter-seat that is arranged opposite the annular valve seat so as to form a slit therebetween. The combined closing-heat protecting element is then movable in this slit between the valve seat and the counter-seat, transversally to the central axis of the annular valve seat, and it is mounted so as to have a degree of freedom parallel to the central axis of the annular valve seat. The means for axially pressing the valve closing element and the annular valve seat together comprises means for axially moving the annular counter-seat. It follows that the combined closing-heat protecting element is sandwiched between the valve seat and the counter-seat when the latter is axially moved in the direction of the annular valve seat. A similar design of the gas-tight shut-off valve may be achieved without using a combined closing-heat protecting element. In this case the soft sealing means is associated with the annular valve seat and the heat protecting element forms an annular counter-seat that is arranged opposite the annular valve seat so as to form a slit therebetween. The closing element is movable in the slit between the valve seat and the counter-seat transversally to the central axis of the annular valve seat, wherein it is located outside the slit when it is in its second position. The means for axially pressing the valve closing element and the annular valve seat together comprises means for axially moving the annular counter-seat. The closing element of this valve has a degree of freedom parallel to the central axis of the annular valve seat, so that it is sandwiched between the valve seat and the counter-seat when the latter is axially moved in the direction of the annular valve seat. It remains to be pointed out that for achieving a gas-tight connection between the axially movable counter-seat and the housing, it is of advantage to use an axial expansion joint, as for example a bellow expansion joint.
If the closing element is pivoted about a horizontal pivoting axis extending laterally of the discharge opening, then the means used for moving the closing element between its first and second position may also be used for pressing the valve closing element and the annular valve seat together. Otherwise, the means for pressing the valve closing element and the annular valve seat together may be associated either with the valve seat for moving the latter relative to the valve closing element or with the valve closing element for axially moving the latter relative to the valve seat. If it is the valve seat that is moved relative to the valve closing element, it is of advantage to use an axial expansion joint, as for example a bellow expansion joint, for connecting the valve seat to the valve housing.
Finally, it will be appreciated that the soft sealing means may be associated with the valve closing element. In this case, the heat protecting element is, in its first position, located in front of the closing element, when the latter is located in its second position.